Hold your drill straight

But seriously, bevery conscious of the angle your drill is on, and keep it the same for the second hole. After the drill is through, wiggle it around a little to enlarge the hole. After all, it's the clamping of the two control horn plates that hold it in place, not the tightness of the holes.

Also, when you screw it in place, don't tighten one and then try to start the other - Get the first one started, then start the other and then tighten them together. Because when the plate is away from the surface, you have more leverage to move the mismatched screw hole.